1. Field of the Invention
This invention relates to a photoconductive member having a sensitivity to electromagnetic waves such as light [herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays and gamma-rays].
2. Description of the Prior Arts
Photoconductive materials, which constitute image-forming members for electrophotography in solid state image pickup devices or in the field of image formation, or photoconductive layers in manuscript reading devices, are required to have a high sensitivity, a high SN ratio [Photocurrent(I.sub.p)/Dark current (I.sub.d)], spectral characteristics matching to those of electromagnetic waves to be irradiated, spectral characteristics matching to wavelength characteristics of light emitted from semiconductor lasers which have recently been particularly developed with a remarkable progress, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during usage. Further, in a solid state image pickup device, it is also required that the residual image should easily be treated within a predetermined time. In particular, in case of an image-forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, amorphous silicon [hereinafter referred to as a-Si] has recently attracted attention as a photoconductive material. For example, German Laid-open Patent application Nos. 2746967 and 2855718 disclose applications of a-Si for use in image-forming members for electrophotography, and German Laid-open Patent application No. 2933411 an application of a-Si for use in a photoelectric conversion reading device.
However, the photoconductive members having photoconductive layers constituted of the a-Si of prior art have various electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and light response as well as environmental characteristics and aging stability in use such as humidity resistance, which should further be improved. Thus, in a practical solid state image pickup device, reading device or an image-forming member for electrophotography, they cannot effectively be used also in view of their productivity and possibility of their mass production.
For instance, when applied in an image-forming member for electrophotography, residual potential is frequently observed to remain during use thereof. When such a photoconductive member is repeatedly used for a long time, there will be caused various inconveniences such as accumulation of fatigues by repeated uses or so called ghost phenomenon wherein residual images are formed.
Further, according to the experience by the present inventors from a number of experiments, a-Si material constituting the photoconductive layer of an image-forming member for electrophotography, while it has a number of advantages, as compared with Se, CdS ZnO or OPC (organic photoconductive materials) such as PVCz or TNF of prior art, is also found to have several problems to be solved. Namely, when charging treatment is applied for formation of electrostatic images on the photoconductive layer of an image-forming member for electrophotography having a photoconductive member constituted of a mono-layer of a-Si which has been endowed with characteristics for use in a solar battery of prior art, dark decay is markedly rapid, whereby it is difficult to apply a conventional photographic method. This tendency is further pronounced under a humid atmosphere to such extent in some cases that no charge is retained at all before development.
Further, the photoconductive members of the prior art exhibit a relatively smaller absorption coefficient in the region of wavelength longer than the long wavelength region as compared with that in short wavelength region of visible light. This means that there is room left to be improved in matching with semiconductor lasers.
Thus, it is required in the designing of a photoconductive material to make efforts to obtain desirable electrical, optical, and photoconductive characteristics along with the improvement of a-Si materials per se.
In view of the above points, the present invention has been obtained as a result of extensive studies made comprehensively from the standpoints of applicability and utility of a-Si as a photoconductive member for image-forming members for electrophotography, solid state image pickup devices or reading devices. It has now been found that a photoconductive member elaborated to have a specific layer structure comprising a photoconductive layer constituted of a so-called hydrogenated amorphous silicon, a halogenated amorphous silicon or a halogen-containing hydrogenated amorphous silicon [hereinafter referred comprehensively as a-Si(H, X)], which is an amorphous material containing at least one of hydrogen atom(H) or halogen atom(X) in a matrix of silicon, and a specific barrier layer interposed between said photoconductive layer and a support which supports said photoconductive layer, is not only practically useful but also has characteristics superior in substantially all respects to those of the photoconductive members of prior arts, especially markedly excellent characteristics as a photoconductive member for electrophotography as well as excellent absorption spectral characteristics in the region of longer wavelengths. The present invention is based on this finding.